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Author Topic: CNC Router "Stutters/Loses Position" on Faster Feed Rates  (Read 2124 times)

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CNC Router "Stutters/Loses Position" on Faster Feed Rates
« on: November 28, 2017, 11:07:41 AM »
I am new to this forum, so I apologize if this is posted in the wrong section or redundant.

Earlier this year I put together my first CNC router. https://www.smw3d.com/r7-cnc-diy-kit/ I used a Mach3 usb board https://buildyourcnc.com/item/electronicsAndMotors-electronic-component-breakout-Mach3-USB-Board with the other components from the kit.

Everything was working great until I started a cutting project that lasted about 1 hour. Running at 30 IPM, it will lose either X or Y positioning and try picking it up again from 1/8" off to 4" off. I also notice that when I bump up the jog rate to 150% for positioning the router, it will stutter or pulsate. Slower feed rates do help eliminate this.

I believe I set up my motors correctly in Mach 3, but has anyone else ran into these issues, or have suggestions on what it could be? It's really frustrating being almost done with a project and then have it ruined because it loses position.

Thanks!

Offline ger21

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Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #1 on: November 28, 2017, 11:49:10 AM »
What are you using for motors, drives, and power supply?

What is the pitch of the leadscrews?

What are your velocity and acceleration settings?
Gerry

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Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #2 on: November 28, 2017, 01:14:06 PM »
Nema 23 2.8A/Phase, 24v 8.3amp power supply, drivers: https://www.amazon.com/gp/product/B016ZJS1FA/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1

Pitch is 2mm.

Velocity and acceleration I'll need to look up when I get to my laptop.
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #3 on: November 28, 2017, 07:39:24 PM »
Simple answer, you are losing steps because of lack of torque at the speed you are trying to run. That comes from motors too small, or motors with high inductance. Nema 24 is a frame size and the range of torque for that size can be 3 or 4 to 1 from one motor to another. A motor with high inductance will greatly reduce the available torque as the speeds go up.

 It can also be from a power supply that is too low of a voltage or actually can’t supply enough current when all three motors move at the same time. Switching power supplies cannot absorb the regenerated power from the motors where an old fashioned linear can. Your screw pitch is also very fine and if it isn’t a ball screw there will be lots of friction losses at higher speed, plus the motor needs to turn much faster.

For comparison I got the lowest inductance motors I could find. They are driven by 80 volt rated drivers supplied by a massive 1500 watt 68 volt linear power supply. The machine has 5mm pitch ball screws and this gives me rapids of 300 ipm and cutting speeds of 200 ipm in plastics and wood. It never misses steps.

The good news is you can incrementaly improve what you have. In order of cost/benefit: 36 power supply would be a good step. Motors with a higher torque rating and lower inductance in the same frame size. Coarser pitch or ball screws.
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #4 on: November 28, 2017, 08:26:26 PM »
Sorry, I was mistaken. It's 8mm/revolution. I have my drivers set at the highest amp (3.5amp). For the steps/rev, I have it set in the 10,000 range in Mach3. The machine has a max feed rate of 240 IPM with a suggested of 60, so I'd expect it shouldn't struggle at all at 30IPM. After all, the machine was designed to cut that fast. My Mach3 velocity is set to 90 IPM, and acceleration to 10 in/sec^2.

Am I setting up the motor tuning in Mach3 correctly? What about the settings on the motor driver? Is it better to have higher or lower pulse/rev?

Thank you all! I value your input greatly!
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #5 on: November 28, 2017, 09:00:42 PM »
Hi,
what number of microsteps?

Craig
My wife left with my best friend...
     and I miss him!
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #6 on: November 28, 2017, 09:15:06 PM »
400 microsteps on the drivers.

I have to be completely honest here, setting this up was completely hit and miss. Knowing what microsteps to pulse/rev ratio to put into Mach3 was guess work. Yes, I did calculate the correct pulse/rev and it is accurate w/in 0.002", which is fine for me and a wood router, but at the end of the day, I went with what sounded didnt make the motor growl at me or go to fast.
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #7 on: November 28, 2017, 09:36:26 PM »
Hi,
is that 400 pulses per rev? That would be called 'half-step'. A normal two phase stepper is 200 pulse/rev.
At 'half step' 400 pulse per rev. At '4 microstep' 800 pulse per rev. At '8 microstep' 1600 pulse per rev.

If that is correct your steps per mm would be 400 (pulse/rev)/ 8 (mm/rev)=50 steps per mm.
If in inch units 50 (step/mm) x25.5= 1270 steps per inch.

Seems like a large discrepency between what you've set and these numbers.

Can you post the manual for your drivers? I suspect, as it stands, there is some confusion between microsteps and pulses
per rev.

Craig
My wife left with my best friend...
     and I miss him!
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #8 on: November 28, 2017, 10:12:03 PM »
Here is the driver I have. If you zoom on it, you will see the pulse/rev on the front of it. I believe I set it at 400, but I could be wrong as I am out of town and away from my machine.
I also attached a screen shot of my mach3 motor setup.
Re: CNC Router "Stutters/Loses Position" on Faster Feed Rates
« Reply #9 on: November 28, 2017, 10:14:36 PM »
Here is a picture of the driver showing the different options. I have it set to the highest amperage, and I believe 400 pulse/rev.